ranger: propagate python3 wchar dependency

ranger: propagate python3 wchar dependency

Fixes:
http://autobuild.buildroot.net/results/da1/da1a4cac055ab4b1a301cf719233ff00d1e793a2/
http://autobuild.buildroot.net/results/8bb/8bbfd91d1d972b5d382e7355a8a36ab532510745/
http://autobuild.buildroot.net/results/05c/05c7691c0cc1ef4cfa842643ab564a3958e66542/
http://autobuild.buildroot.net/results/dfd/dfdbb574708393b627b1244a627444478155c70f/

Python3 needs wchar, so ranger needs to depend on that as well before we can
safely select python3.

While we're at it, also add a comment about the toolchain dependencies.

Signed-off-by: Peter Korsgaard <peter@korsgaard.com>